1. Field of the Invention
The present invention relates to an ion implantation apparatus.
2. Description of the Related Art
In a semiconductor device manufacturing process, an important process for making the semiconductor wafer into a semiconductor device is performed by adding impurities to a crystal of a semiconductor wafer using method of implanting ions into the semiconductor wafer in vacuum to change conductivity. An apparatus used in this process is referred to as an ion implantation apparatus that generally implants ions into a semiconductor wafer by accelerating impurity atoms as ions for making a semiconductor device.
Recently, with high integration and high performance of the semiconductor device, there is a need for higher performance to realize high-energy ion implantation for implanting ions into a deeper portion of the semiconductor wafer. In order to realize such high performance, for example, there is a method of configuring an ion beam acceleration system with a tandem-type accelerator.
Also, a conventional single-wafer type high-energy ion implanter is intended to implant a uniform amount of high-energy ions at a uniform angle on an entire surface of the wafer by using a Van de Graaff type tandem accelerator or a heavy ion linear accelerator (linac) in an acceleration unit and using a filtering magnet (for valence separation in the case of the tandem, and for energy analysis in the case of the linac), a beam scanner (device for generating a scan beam by a low-frequency electric field or magnetic field), and a magnetic field collimating magnet (electromagnet for collimating a scan trajectory of a scanned beam from a center trajectory in alignment with a central trajectory direction), which are provided in a downstream. Ion energy is about 3 to 4 MeV.
If high-energy ions are implanted into a wafer with a photoresist, a large amount of outgas is generated, and a valence of some ions is changed by the interaction between gas molecules of the outgas and beam ions. If the valence is changed during passage of the magnetic field collimating magnet, a deflection angle of collimation is changed, and thus an implantation angle to a wafer is not uniform. Also, the amount (number) of ions implanted is calculated by measuring a beam current value in a Faraday cup disposed near a wafer. However, the measured value fluctuates out of an expected implantation value according to the change of the valence, and thus characteristics of a semiconductor device are not obtained as expected. Also, since the collimation by the magnetic field (collimator magnet) has different deflection angles and trajectory lengths in an inner trajectory and an outer trajectory, the ratio of ions whose valence is changed increases toward the outer trajectory, degrading implantation uniformity within a wafer plane.
Also, the magnetic field collimating parallel magnet requires a wide magnetic pole in a scan direction and a relatively long collimation section. As energy is higher, the magnetic pole also becomes longer and larger and the weight significantly increases. Therefore, in order to safely install and maintain the apparatus, it is necessary to reinforce a strength design of a semiconductor factory itself, and power consumption significantly increases.
On the other hand, a portion of a single-wafer type medium-current ion implanter having relatively lower energy than the single-wafer type high-energy ion implanter uses an electrostatic (electrode type) parallel lens and an electrostatic (electrode type) energy filter (angular energy filter (AEF)) in order to avoid the drawbacks of the parallel electromagnet. The electrostatic parallel lens collimates a scan trajectory in alignment with a central trajectory direction while maintaining the symmetry of trajectory, and the AEF removes ions whose valence is changed immediately before the wafer. Therefore, even when a large amount of outgas exists, a beam having no energy contamination can be obtained, and a variation in implantation angle in a scan direction such as the magnetic field collimating parallel magnet does not occur. As a result, it is possible to uniformly implant ions having an exact implantation distribution in a depth direction and an exact implantation amount (dose), and the implantation angle is uniform. Thus, ion implantation having very high accuracy is realized. Also, a lightweight electrode member is used, and power consumption is small as compared with the electromagnet.
However, when the beam ions are deflected toward the same angle, a required magnetic field is in proportion to a square root of energy, whereas a required electric field is in proportion to energy itself. Therefore, since the length of the deflection magnetic pole in the magnetic field collimation is in proportion to the square root of the energy but the deflection electrode in the electric field collimation is lengthened in proportion to the energy, the beam transport system (distance from the scanner to the wafer) becomes relatively long when intending to realize the high-accuracy angle implantation in high-energy ion implantation. Also, it is necessary to supply an electrode with a voltage having very high accuracy and stability, but a voltage dynamic range required to an electrode power supply in the electric field collimation in order to cover an implantation energy range from low energy to high energy is much wider than a current dynamic range required to an electromagnet power supply in the magnetic field collimation.
When the advantage of the collimation angle accuracy of the medium-current ion implanter including such an electric field collimating mechanism is introduced to the high-energy ion implantator, for example, it may be considered a configuration in which constituent devices, such as an ion source, a mass analysis magnet, a tandem type accelerator or a radio-frequency linear accelerator (linac), a downstream beamline being a beam transport system including an energy filter, a beam scanner, a collimator, a final energy filter, an implantation processing chamber, and a substrate transfer device (end station), are fixed independently and in a substantially straight line. However, in this case, the total length of the apparatus becomes very long, setting and preparation of an installation site, installation work, and the like become complicated, and the installation area is also increased. Also, adjustment of fixing alignment of each device, maintenance or repair of the apparatus after the operation, and work space for adjustment are also required. Such a large-scale ion implanter cannot satisfy requirements for adjusting the apparatus size in the semiconductor manufacturing line to the actual circumstances of the production line arrangement of the factory.